80% and 90% pure acid solutions are mixed obtain 20 litres of 87% pure acid solution. Find the quantity (in litres) of 80% pure acid solution taken to form the mixture.

6

Using mixture and allegation method,

⇒ So, ratio of quantity of 80% and 90% of pure acid in the solution = 3 : 7

⇒ So, 80% pure acid = 20 x \(\frac{3}{10}\)

⇒ 6 litres.